Conventional spark plugs for internal combustion engines, such as an automobile engine, include a central electrode and a ground electrode. There has been a continuing demand for a material to be used for the central and ground electrodes of a spark plug which has such characteristics as a favorable oxidation resistance in the high temperature environment of a spark plug, less spark erosion, favorable thermal conductivity, high durability at high temperatures, favorable machinability and the like. For the ground electrode, a particular characteristic that is in demand is favorable weldability. Currently, the material generally employed in attempting to satisfy these demands is a heat-resistant nickel (Ni) alloy.
There has been disclosed in the prior art (see, e.g., Japanese Patent Application Laid-Open (kokai) No. 2002-235138) a heat-resistant nickel alloy which contains: chromium (Cr) in a range from 10 to 25% by weight; iron (Fe) in a range from 0.5 to 10% by weight; aluminum (Al) in a range from 0.3 to 3.2% by weight; silicon (Si) in a range from 0.2 to 2.2% by weight; manganese (Mn) in a range from 0.1 to 0.8% by weight; magnesium (Mg) less than 0.001% by weight; sulfur (S) less than 0.002% by weight; and which further contains nickel (Ni) and indispensable impurities as the remainder. By using such a nickel alloy material containing a relatively high Cr content, the oxidation resistance, which is attributed to a Cr oxide film formed on the surface of the corresponding electrode, is improved.